Interference was observed in interference chamber where air was present, now the chamber is evacuated, and if the same light is used, a careful observer will see (a) no interference (b) interference with brighter bands (c) interference with dark bands (d) interference with larger width

Answer: (d). Refractive index of air is slightly more than 1, so in vacuum the wavelength λ = μairλair is slightly larger. β = (λ D)/(d) ∝ λ, so the fringe width increases slightly. So the answer is (d) interference with larger width.

Interference was observed in interference chamber where air was… | NEET 1993 (AIPMT)

Q72NEET 1993 · AIPMTEasy

YDSE: Film, Medium & Two Wavelengths

Interference was observed in interference chamber where air was present, now the chamber is evacuated, and if the same light is used, a careful observer will see

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Answer: (d)

Refractive index of air is slightly more than 1, so in vacuum the wavelength $\lambda = \mu_{air}\lambda_{air}$ is slightly larger.
$\beta = \frac{\lambda D}{d} \propto \lambda$ , so the fringe width increases slightly.
So the answer is (d) interference with larger width.

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YDSE: Film, Medium & Two Wavelengths question from NEET 1993 (AIPMT)

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